Hydrocarbon fluids, including liquids and gases, are found in geologic formations located below the earth's surface. Generally, these hydrocarbon fluids are mixed with other impurities that are undesirable. One of these impurities is sulfides, in particular, sulfhydryl compounds including, but not limited to hydrogen sulfide (H2S). The presence of hydrogen sulfide and other sulfhydryl compounds is objectionable because these compounds may react the hydrocarbon fluid, are often corrosive, flammable, poisonous and emit a noxious odor. Due to the noxious odor, hydrocarbon fluids containing hydrogen sulfides and/or other sulfhydryl compounds are often called “sour” hydrocarbons.
The removal of hydrogen sulfide and/or other sulfhydryl compounds from liquid or gaseous industrial process streams is a challenge in a wide range of industries, particularly in the oil and gas production industry. The presence of hydrogen sulfide poses significant environmental and safety concerns to personnel and operations, and can make the hydrocarbon fluid unacceptable for commercial purposes This is due in part to the fact that hydrogen sulfide is highly flammable, highly toxic when inhaled (8 h of exposure at 100 ppm has been reported to cause death while levels of 1,000 ppm can cause death within minutes), highly corrosive, and malodorous. Further, corrosion and scale deposits resulting from the presence of hydrogen sulfide in contact with metallic surfaces, such as carbon steel pipes can further disrupt industrial operations via the plugging of pipes, valves, nozzles, and the like.
In the oil and gas industry, the removal of hydrogen is important for the transport of gas as well as the transport and storage of crude reserves in order to meet quality standards for either delivery or downstream refining. The latter is an important consideration due to sulfide poisoning of cracking catalysts. Further, in both the refining industry and geothermal power industry, cooling tower process water can contain moderate to high levels of hydrogen sulfide, both causing significant solids development, as well as increasing the level of oxidant demand so as to make oxidants unviable options for microbial control in these systems.
Nonetheless, the challenge of removing and/or reducing hydrogen sulfide and other sulfhydryl compounds from hydrocarbon streams has been addressed with a variety of different technologies. These processes are often call “sweeting” of the hydrocarbon fluid. Components added to hydrocarbon fluids to reduce or eliminate hydrogen sulfide or sulfhydryl compounds are commonly called a “scavenging agent” or a “scavenger”. Common techniques utilize either absorption with a solvent or solid phase material with subsequent regeneration of the absorbent, or reaction with a suitable substance or substrate “scavenger” that produces a corresponding reaction product.
In the past, several different methods of reacting hydrogen sulfide and/or sulfhydryl compounds present in fluid streams have been used. The reaction has often involved the reaction of hydrogen sulfides with various types of aldehydes. For instance, U.S. Pat. No. 1,991,765 was an early example describing the reaction of formaldehyde with hydrogen sulfide to form an insoluble product, later identified as the sulfur heterocycle 1,3,5-trithiane. Other examples include U.S. Pat. No. 2,426,318, which discloses a method of inhibiting the corrosivity of natural gas and oil containing soluble sulfides by utilizing an aldehyde such as formaldehyde. U.S. Pat. No. 3,459,852 discloses a method for removing sulfide compounds with α,β-unsaturated aldehydes or ketones such as acrolein or 3-buten-2-one (methyl vinyl ketone) as the reactive compounds. Nonetheless, both acrolein and 3-buten-2-one are hazardous, highly toxic chemicals limiting extensive use in a wider variety of applications. U.S. Pat. No. 4,680,127 describes a method for reducing H2S in a neutral to alkaline aqueous medium (pH˜7-9) without the formation of solids (a problem when using formaldehyde), using glyoxal or mixtures of glyoxal and formaldehyde or glutaraldehyde. However, the glyoxal/formaldehyde mixtures exhibited slower rates of hydrogen sulfide scavenging than glyoxal alone.
Other methods of scavenging hydrogen sulfide have been described. In U.S. Pat. No. 4,978,512 describes a method where an alkanolamine and an aldehyde are reacted together to form a triazine, which is used to scavenge hydrogen sulfide. U.S. Pat. No. 5,498,707 describes a composition wherein a diamine and an aldehyde donor is used to scavenge hydrogen sulfide from liquid or gaseous process streams. U.S. Pat. No. 7,438,877 discloses a method for sulfide removal utilizing mixed triazine derivatives for improved scavenging. The mixture improves the overall scavenging capacity of triazines, but whether complete removal is achieved for a theoretically stoichiometric amount is not reported. However, it is known that typically triazines, such as hydroxyethyl triazines, do not scavenge H2S stoichiometrically (i.e., 3 mol of H2S per mol triazine) due to formation of cyclic thiazines that do not further react with H2S (Buhaug, J.; Bakke, J. M. “Chemical Investigations of Hydroxyethyl-triazine and Potential New Scavengers”, AlChE 2002 Spring National Meeting).
Although multiple methods have been developed for scavenging hydrogen sulfide and/or sulfhydryl compounds from hydrocarbon fluids, including those hydrocarbon fluids from oil and gas production systems, each of these methods and compositions have drawbacks. These drawbacks include, for example, the formation of compounds that participate in aqueous environments, such as trithianes that are produced when sulfhydryl compounds are reacted with formaldehyde. In the case of triazines that release formaldehyde, these compounds also release alkyl amines which can raise the pH in the system, potentially leading to scale deposition. In addition, triazine compounds, such as the commonly used 1,3,5-tris (2-hydroxyethyl)-hexahydro-s-triazine, is considered to be highly toxic and corrosive. As such, this compound has many drawbacks.
In addition, the use of downhole injection of scavenger is limited often by either the inherent thermal and chemical instability of the scavenger, the generation of inorganic scale products due to pH changes, and/or the generation of solid by-products such as elemental sulfur, as in the case of sodium nitrite. Hence, in order to prevent problems associated with hydrogen sulfide and other sulfhydryl compounds in the production system and to improve the quality of the oil and gas produced, it is desirable to be able to use the chemical as early as possible in the production process, such as via downhole injection. There remains a need for a safe and effective means to effectively scavenge hydrogen sulfide and/or other sulfhydryl compounds from hydrocarbon fluids. Ideally, the scavenge for hydrogen sulfide should be non-hazardous, non-corrosive, biodegradable, and have a scavenging performance over a wide temperature range and pH range. The present invention provides an answer to that need.